UDP-glucuronosyltransferase (UDPGT) is a membrane-bound enzyme that participates in the metabolism of potentially toxic foreign (xenobiotic) and endogenous compounds. This enzyme catalyzes the transfer of a glucuronyl group from the substrate UDP-glucuronic acid (UGPGA) to a variety of acceptor molecules, or aglycones. The aglycone is solubilized, which facilitates its excretion from the body. A simplified kinetic mechanism for UDPGT has been proposed, but the molecular details of the reaction are not well understood. Bacterial and baculoviral expression systems will therefore be developed for the rat phenol enzyme. Based on sequence alignments with other forms of UDPGT, conserved amino acids will be targets of site-directed mutagenesis. Native and mutant enzymes will be kinetically characterized and the conformational and stereoselective properties of the enzymes will be evaluated by using specific substrates.